<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>类选择器</title>
    <style>
        .c2{
        height: 50px;
        color: orange;
}
    </style>
</head>
<body>
<h1 class="c2">用户登录</h1>
</body>
</html>